Polygraph testing has nothing to do with the scientific legitimacy of the actual instrument used. It's just an interrogation technique. Using it effectively is

Polygraph testing has nothing to do with the scientific legitimacy of the actual instrument used. It's just an interrogation technique. Using it effectively is all about the skill of the person administering the test, and their ability to judge the person being tested. It is just one part of building a profile of whether you think someone is lying or not. The purpose of the test is to put someone through a highly stressful situation and see how they react to questioning. It's about determining whether they've been coached, and how familiar they are with details of the case, not determining a definitive "yes/no" response to specific questions. Polygraph questions can be passed with 100% accuracy by someone with extensive training, so it's entirely about building a gut feeling in the person administering the test as to whether you are lying or not.